Optical communication devices are used for transmitting and/or receiving optical signals used for optical data communication. Prior to transmission, the optical signals are generated by a light source, for example by a laser diode. Optical signals transmitted are received by an optical receiver such as a photo diode. Transmission of optical signals may be performed by an optical fiber cable comprising one or more optical fibers.
For guiding optical signals between an optical transmitter/receiver (transceiver) and an end portion of an optical cable a so-called optical coupling devices or optical coupling unit may be used. Within the optical coupling device an optical signal path is provided between optical ports of the optical coupling device. One of the optical ports is configured for receiving the optical signals from the optical transmitter and/or for transmitting the optical signals to the optical receiver. Another optical port of the optical coupling device which is connected to the optical port by the optical path is configured for receiving the optical signals from and/or for transmitting the optical signals to the optical fiber.
In optical communication devices, a (partially) transparent coupling unit may be used for beam or signal guidance and/or building an optical signal path by using lenses and reflective optical surfaces. If the optical signal, for example, is generated by a laser device, it might be necessary to control or monitor the optical output power of the laser. For implementation of such monitoring feature, a part of the optical signal is coupled out to a photo diode, which may also be referred to as monitor diode, in order to measure the present optical output power of the laser by an electronic circuit. The monitor diode is often located in close vicinity to the laser on the same surface (substrate) as the laser.